This invention relates to a stent for use in body passages and more particularly, to a stent having at least one end which is coated or to a stent having at least one end which is treated to be smooth and flexible. The invention also has particular relevance to a stent having at least one end coated where the coating consists at least in part of drugs for delivery.
Stents are used in human or animal body passages for maintaining the patency of the passages. Stents are generally tubular in configuration, open ended and are expandable between a generally unexpanded insertion diameter and an expanded implantation diameter. Stents are commonly placed or implanted by a mechanical transluminal procedure.
Prior art patents refer to the construction and design of stents as well as apparatus for positioning stents within a vessel or other passage. In general, for example, such patents disclose a technique for positioning an elongated cylindrical stent at a region of stenosis, an aneurysm, or the like. The stent expands as necessary to an implanted configuration after insertion with the aid of a catheter.
Specifically, U.S. Pat. No. 4,733,665 to Palmaz discloses a number of stent configurations for implantation with the aid of a catheter. U.S. Pat. No. 5,019,090 to Pinchuk discloses a generally cylindrical stent and technique for implanting it using a deflated balloon catheter to position the stent. U.S. Pat. No. 4,503,569 to Dotter and U.S. Pat. No. 4,512,338 to Balko et al. disclose a spring stent and a shape memory alloy stent. There are also self-expanding stents such as those described in U.S. Pat. No. 4,732,152 to Wallsten et al. and U.S. Pat. No. 4,848,343 to Wallsten et al. All of these patents are hereby incorporated by reference.
It is important that the placement of the stent not contribute to or cause additional blocking. It is known that when stents are expanded to their implantation diameter the ends of the stent may press into the vessel or cavity walls, especially the distal end of the stent. The sharp or pointed edges and ends of some stents may then damage the walls. Once damage has occurred, there is a likelihood that restenosis will occur at these points where the stents ends and edges have penetrated or pressed against the walls.
It is also known that stents may tear a passage wall and contribute to restenosis. This is particularly important for use of stents in blood vessels. A tear in the vessel wall may cause blockage of the vessel. When the wall is torn a flap of tissue is created. The torn wall or flap usually is the source of the blockage. The flap falls into the passage and blocks it. It is then necessary to perform another procedure to remove the blockage and generally, another stent is needed to open the vessel or other passage.
Restenosis occurs in a number of cases where a stent has been used. Tearing of the wall of the passage or injury of the endothelial cell layer are possible causes of the restenosis. Therefore, it is desirable to utilize a stent which reduces the chances of a damaged vessel wall or body passage which leads to further problems and further necessary procedures. However, current stents are not designed to reduce the occurrence of cutting of vascular passages or the like.
In addition, it is known that a number of drugs may reduce the chance of restenosis. Therefore, the use of these drugs in combination with a stent designed to reduce damage to body passages would be advantageous. However, known stents are not utilizing drugs with a means for reducing damage to vessels and the like.
It is also known that bioadhesives may be used to repair tissue walls which may have been torn. However, current stents are not designed to avert a potential problem due to a tear. Currently, stents are not utilizing a bioadhesive with a stent to repair tissue walls and prevent further medical procedures required because of the dissection of a body passage.
Consequently, a need remains for a stent which reduces the chances of a tear or other damage of a body passage and which lessens the chances of further required procedures. The present invention provides a stent which reduces the limitations of the prior stents with regard to possible tearing and the need for further treatment and therefore, performs in an improved fashion.
In accordance with a preferred embodiment of this invention a stent is characterized in that it includes at least one end coated with a desired material or materials. The coating may be of any desirable type which lessens the chance of a tear in the passage, generally a coating with a smooth finish is preferred. Generally, any prior art stent may be improved by providing it with a coating layer or layers of polymeric composition on at least one end to provide a smooth finish. For another type, a stent may be provided with a sleeve which may be connected to one or both ends of the stent.
In another embodiment, the stent which has been coated or the stent which utilizes a sleeve may include bioadhesives and/or drugs to be delivered to the site where the stent is implanted. It is known that bioadhesives can be used to repair tissue walls. It is therefore desirable to utilize a polymer coating to carry and deliver a bioadhesive to the stent implantation location. In this manner, a potential problem can be averted by the presence of the bioadhesive in the case of a tear or dissection. It is further known that a number of different drugs can be useful if delivered to the stent site. It is desirable to deliver the drug or drugs with the stent when implantation is occurring or has occurred.
For yet another embodiment of the invention a stent is characterized in that at least one end is constructed in a manner such that the end is treated to be smooth and flexible. The stent material may be heat treated, for example, or the design of the stent may be such that it provides for flexibility on an end. Another embodiment includes a stent designed such that a looser mesh or pattern is utilized on the end or ends of the stent and a tighter mesh or pattern is utilized in the middle portion of the stent. These stents may also be coated on one or both ends as well as materially treated.
Yet another embodiment of the invention a stent is constructed of varying materials having different degrees of flexibility. A more rigid material is used in the center portion of the stent and a more flexible material is used for one or both of the end portions of the stent. This embodiment may also be materially treated to increase smoothness or flexibility and may also be coated.
Stents according to the invention may be self-expanding or of the type which are expandable from a reduced diameter configuration by an exterior force (as opposed to self-expanding). The expandable stents may be balloon expanding for example. Both types of stents are well known in the art and need not be described in additional detail herein.
Stents according to this invention may be metal stents or polymeric stents, the stent providing the basic framework for the device.
These and other advantages and features which characterize the invention are pointed out with particularity in the claims annexed hereto and which form a further part hereof. However, for a better understanding of the invention, its advantages and objects obtained by its use, reference should be made to the drawings which form a further part hereof, and the accompanying detailed description in which there is shown and described an illustrative embodiment of the invention.